The present invention relates to a new and improved construction of a gas-blast switch.
Generally speaking, the gas-blast switch of this development is of the type comprising a movable contact element which is coupled by means of a step-up lever drive with a drive rod, and a blast nozzle which is co-movable with the movable contact element and surrounds the latter. The blast nozzle is connected with a pump cylinder containing an extinguishing gas, this pump cylinder being displaceably guided upon a pump piston. The pump piston is hingedly connected with one end of a first element of a toggle lever which in the cut-on position is in its bent position. A second element of the toggle lever is hingedly connected with a stationary location or point and the toggle joint of the toggle lever likewise is coupled with the drive rod, so that during a cut-off stroke the toggle lever is extended and then again bent.
Such type gas-blast switch is known, for instance, from German Pat. No. 1,966,973. With this switch the drive rod extends transversely with respect to the displacement direction of the assembly composed of the movable contact element, the blast nozzle and the pump cylinder. This assembly or unit is coupled by means of a rocker arm with the longer arm of an angle lever which is pivotably mounted at a stationary pin, the shorter arm of such angle lever being coupled by means of a coupling element or link at the drive rod. The toggle lever, at which there is coupled the pump piston, in the cut-on position is in a bent position directed away from the drive rod, and its toggle joint is connected by means of a further coupling element with such drive rod.
The construction of the heretofore known gas-blast switch operates such that between the movement of the drive rod and that of the movable contact element (together with the blast nozzle and pump cylinder) there is present a practically constant transmission which is governed by the length difference of the arms of the angle lever. On the other hand, the drive rod, immediately at the start of the cut-off stroke, pulls the toggle lever into its extended position, i.e. the pump piston moves immediately at the start of the cut-off stroke opposite to the cylinder, and only after there has been exceeded its extended position does it begin to move in the same direction as the pump cylinder.
Immediately at the start of a cut-off stroke the drive which drives the drive rod simultaneously must perform the following work. First of all, the movable contact element and the parts which co-move along therewith, such as the blast nozzle and cylinder, must be accelerated out of their stationary state. Secondly, during the opposite movement of the pump piston in relation to the cylinder there must immediately at the start be compressed the gas which is present in the cylinder, so that a short time later compressed extinguishing gas is available for blowing the switching arc.
However, it is strived that just at the start of the cut-off stroke the acceleration of the movable parts should have as high a value as possible, whereas the compression of the extinguishing gas should not start immediately at the beginning of the cut-off stroke, since the compressed extinguishing gas only must be available during a later point in time of the cut-off stroke, namely then when the increasing spacing of the movable contact element with respect to the stationary contact element, with which it was in engagement, approaches the minimum extinguishing distance.